Stable high-temperature superlubricity enabled by thermomechanical-induced interfacial graphitization and SiOx-mediated structural locking

Abstract

Achieving stable superlubricity of diamond-like carbon (DLC) films in air at elevated temperatures remains a critical challenge due to thermally driven hydrogen loss and oxidation-induced structural degradation. In this work, we demonstrate that silicon-doped hydrogenated amorphous carbon (a-C:H:Si) films exhibit robust superlubricity (μ ≈ 0.002) at 300 °C in atmospheric air. In situ Raman and fourier transform infrared spectroscopy (FTIR) analyses reveal that oxygen accelerates hydrogen desorption, generating active dangling bonds that facilitate thermomechanical-induced graphitization during sliding. Simultaneously, silicon reacts with oxygen to form a SiO_x interfacial layer that stabilizes the high-sp² tribofilm and prevents excessive structural collapse at elevated temperatures. Transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) results confirm the formation of a transferable tribofilm consisting of graphite-like layers and carbon-onion nanostructures, which provides a low-shear sliding interface. This work identifies the synergistic role of oxygen-driven graphitization and SiO_x-mediated structural locking in enabling high-temperature superlubricity, offering a general strategy for designing solid lubrication coatings for extreme environments.